Encapsulated variable inductor



Aug. 13, 1963 ENCAPSULATED VARIABLE INDUCTOR N. BURNELL l 3,100,882

Filed Feb. 26, 1960'v N FHNW l :'i

Co., Inc., Pelham Manor, NX., a `corporation of New y York l Filed Feb.26, 1960, Ser. No. 11,323 2 Claims. (Cl. 336+96) This invention isconcerned with inductors, particularly e -toroidal coils, and aims toprovide simple economical in- UnitedStates Patent O ductors in which theinductance can be varied rapidly over a wide range, and which `arecharacterized by sirnplicity of construction yand extreme resistance tooutside influences.

` A ygreat deal of research! has been done in recent years on Itheprovision Tof toroidal coils whose characteristics can be changed over awide range by the use of biasing fluxes induced by magnets. Aparticularly satisfactory device of this sort is disclosed in the GordonPatent;- 762,020,'issued September 4, 1956. In such ya device, a

toroidal coil comprising a ferromagnetic annulus with a toroidal windingist combined with a pair of bar magnets which are mounted on oppositefacesof the toroid. One

of thevmagnets is mounted fixedrelationship to the toroid across itsdiameter :adjacent oneface, `and the other magnet is preferably mountedadjacent the other Iface for rotation about the axis of the coil, sothat it can beV swung around from 3a vposition where the like poles ofthe magnets are directly `facing each other, to a pointwhere theopposing poles of the magnets are directly facing each other. Inthe'position where opposite poles.` are facing each other, there isrelatively little magnetic iiux through the coil, since the flux passesdirectly yfrom one north y pole to the opposite south pole through avery small vcrosss'ection of the tor-oid, then goes through -the othermagnet and back intothe original magnet through another smallcross-section ofthe toroid. When the like poles lare facing each other,however, the magnet ilux is forcedV to go parts and yet is extremelyeasy to yadjust from a position of induction to a position of maximuminduction.

Still another object of the invention is the production of an assemblyof this sort which can be made rapidly and at low cost, and Itheprovision of a proce-ss for so doing.

These and other objects can be obtained, according to this invention byencapsulating. a` toroidal coil inductor with a magnet below it inasingle unit, together with a double headed bolt, one head of which isencapsulated in the unit and the other head of which protrudes on theside of the assembly which is adjacent the coil. rThe free head is thenencapsulated together with another fixed permanent bar magnet in alsimi-lar unit. One head of the bolt is lixedly embedded in theencapsulating material, and the other head of the bolt is prevented fromadhering to the encapsulating material by |any treatment which willensure parting. The result isa-completely encapsulated variable toroidalco-il in which one of the units can be rotated about its encapsulatedbolt headv by Yreason of the failure of the encapsulating material toadhere to the bolt head.

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rllhe invention can be best understood by referring .to the accompanyingdrawings, which are provided here by way of illustration and not by Wayof limitation. In the drawings, Y Y s FIG. l is a perspectivev ofthefinished variable inductor.

FIG. 2 is a vertical section through the center of the inductor.

FIG. 3 is a schematic elevation showing ythe flux'distribution through'the inductor at the position of maximum biasing flux.

FIG. 4 is a `schematic plan view of FIG. 3.

FIG. 5 is a schematic elevation showing the flux distribution at thepoint of minimum biasing flux.

FIG. 6 is a schematic plan view of FIGS. Referring to FIGS. 1 and 2 ofthe drawings, the device comprises a cylinder 10 mounted on a secondsomewhat longer cylinder 12, out of which lead wires 14 protrude. Thecylinder 10 can be rotated coaxially with ycylinder 12, as by means of ascrew driver inserted slot 13. Preferably .the cylinders are separatedby la mere hairline division The device is `actually made from a pair ofplastic conf cen-tric cylindrical cups or housings 16r and 18, mounted vwith their blases 17-19 flush against each other, so they `are`separated by a mere hairline 15. A hole 20' is drilled through bothbases, at the axis of the cylinders. A rivet 21 with a head 22 isinserted inthe hole; the rivet head 22 is coated with a film 23 of somematerialwhich prevents the adhesion of the potting material later used.Thebottom of the rivet 21, after insertion in the hole, is peened overto Iform ,-a second head 24, which holds the two cups firmly together;

-A magnet 25 is then'dropped into the cupy 16, and the cup filled with apot-ting compound 26, which has desirablepelectrical characteristics,Known desirable potting compounds include the epoxy resins, unsaturatedpolyester resins, diallylphthalate polymers and the like. The lm 23,which prevents the adhesion of the potting compound,

may be of any lcnown parting agent. The silicone oils (for example,Dow-Oornings DC20 and DCZOO) are quite satisfactory for use with epoxyresin potting compounds. Wax -lms and the solid fatty acids may also beused, with low temperature potting compounds.

After the potting compound 26 has `set and ith-us the magnet 25 has beenhermetically sealed in cup or housing 16, as shown in FIGURE 2, thehousing containing the magnet is inverted. An inductor 28 is placed inthe cup 1S adjacent'its base 19; it comprises a core 29 with windings30, to which are attached the lead wires 14. The cup is then preferablyfilled with potting compound 32 to just cover the coil, and a magnet253` is dropped in. Thus,

the magnet is immediately adjacent the coil, being separat-ed therefromonly by as much potting compound -as is not squeezed tout; the amountwill vary as desired with the :consistency of the potting compound. Thecup 18 is then filled with potting compound, and the device is 'treatedas desired to complete the hardening of the potting compound, thushermetically sealing inductor 28 and magnet 33t within the cup orhousing 1S, as shown in FIGURE 2. A slot 13 may then be cut in the topof the hardened potting compound 26 to permit rotation with a screwdriver.

As illustrated, the entire `section Yenclosed in the cup 16 rotates as aunit about the rivet head 22, land the inductance of the device may bevaried from one extreme to the other by rotating through as shown inFIGS.

3 to 6. Obviously, the parting film 23@` could be on the l toA bedirectly attacked by outside influences. `devic'elends itself to useunder all sorts of conditions,

compound, so that after the potting compound is completely hardened, theunits Iare essentially homogeneous hardened potting compound enclosingthe metallic parts 4of the device. This makes' for loptimum,electricaluni- `forrnity.

It'will be noted that the working elements are com.-

`pletely protected Yelectrically and mechanically, to provide a verysimple rugged unit with no exposedworking parts Thus, the

where an ordinary mechanical combination of the -uni-ts would besusceptible to extensive damage.

K 'Another great advantage of the device is in usev with circuits wherethe exact inductance needed cannot be exactly predicted in advance, andit is necessary to tunethe inductance to a desired optimum setting. Thiscan readily be'done with the instant device, and the two cups 16 and 18cemented together with more potting compound, to produce a completelysealed and homogeneously encapsulated unit.

Obviously, the specific ilonm` of the invention herein disclosed can bemodified extensivelyvwithout departing from the scope ofthe invention asdefined in the claims.

What is claimed' is: 1. A variable toroidal coil inductor consistingessentially of a first t ousing having side walls anda base, a 'magnettcentrally positioned in said housing, extending 'substantially acrosstheV width thereof, a potting comthe said base and held in said positionby the other head of said double headed rivet, which rivet passesthrough a central opening in said top and hasthe other head thereofpositioned to securely hold the said top and said hase in substantiallyabutting relationship, |a toroidlal coil disposed in said second housingimmediately adjacent said top, a second magnet positioned adjacent ysaidtoroidal coil and extending substantially across the width of saidsecond housing, potting `compound in said second housing encapsulatingthe second-mentioned magnet, said tonoidal coil and saidsecondnnentioned magnet being'hermetioally `sealed within said secondhousing by the potting c0m pound therein, and lead wires from said lcoilextending through the potting compound in said second housing externallyof said second housing.

2. A variable inductor comprising two cylindrical cups,

each containing a matrix :of insulating materiahthe said cups having acommon axis and the base of one cup being in substantial contact withthe base of the other cup, the said other cup having its side Walls inlongitudinal align- `ment and extending in the opposite direction fromthe side walls of the said one cup, la shaft positioned on the commonaxis passing through the yadjoining bases of said cups and thus asteningthe two cups, yfor pivotal movement of one cup relative to the other,the shaft having a head firmly embedded inand attached to one matrix in"one cup and a head embedded inwbut not attached to the matrix intheother cup, whereby the said relative pivotal movement about the commonaxis can be eliected, a magnet embedded in the matrix in one cupextending diametrically across said cup immediately adjacent lthe baseof said cup, a toroidlal coil embedded in Kthe matrix in the other cupcoaxially with said cup adjacent its hase, -a magnet embedded in thematrix of the said other cup adjacent said coil extending diametricallyacross the said other cup, and lead wires leading from the vcoil throughthe matrix 'in Ithe said other cup.

References Cited in the le of this patent UNITED STATES PATENTS2,731,607 Gould 1an. 17, 1956 2,762,020 Gordon sept. 4, 1956 2,775,742Bogue Dec. 25, 1956 2,887,729 Imhof May 26, k1959 2,948,930 VHellllste.. Allg. 16, 1960

1. A VARIABLE TOROIDAL COIL INDUCTOR CONSISTING ESSENTIALLY OF A FIRSTHOUSING HAVING SIDE WALLS AND A BASE, A MAGNET CENTRALLY POSITIONED INSAID HOUSING, EXTENDING SUBSTANTIALLY ACROSS THE WIDTH THEREOF, APOTTING COMPOUND ENCAPSULATING SAID MAGNET AND FILLING SAID HOUSING ANDTHUS MAINTAINING SAID MAGNET CENTRALLY POSITIONED RELATIVE TO SAIDHOUSING AND HERMETICALLY SEALED WITHIN SAID HOUSING, A DOUBLE HEADEDRIVET HAVING ONE HEAD CENTRALLY DISPOSED RELATIVE TO SAID BASE,EXTENDING THROUGH AN OPENING IN SAID BASE AND POSITIONED IN THE PORTIONOF SAID POTTING COMPOUND ADJACENT SAID BASE FOR PIVOTAL MOVEMENT OF SAIDFIRST HOUSING RELATIVE TO SAID RIVET, A SECOND HOUSING HAVING SIDE WALLSAND A TOP IMMEDIATELY ADJACENT THE FIRST HOUSING, WITH THE SAID TOPPOSITIONED CONTIGUOUS TO THE SAID BASE AND HELD IN SAID POSITION BY THEOTHER HEAD OF SAID DOUBLE HEADED RIVET, WHICH RIVET PASSES THROUGH ACENTRAL OPENING IN SAID TOP AND HAS THE OTHER HEAD THEREOF POSITIONED TOSECURELY HOLD THE SAID TOP AND SAID BASE IN SUBSTANTIALLY ABUTTINGRELATIONSHIP, A TOROIDAL COIL DISPOSED IN SAID SECOND HOUSINGIMMEDIATELY ADJACENT SAID TOP, A SECOND MAGNET POSITIONED ADJACENT SAIDTOROIDAL COIL AND EXTENDING SUBSTANTIALLY ACROSS THE WIDTH OF SAIDSECOND HOUSING, POTTING COMPOUND IN SAID SECOND HOUSING ENCAPSULATINGTHE SECOND-MENTIONED MAGNET, SAID TOROIDAL COIL AND SAIDSECOND-MENTIONED MAGNET BEING HERMETICALLY SEALED WITHIN SAID SECONDHOUSING BY THE POTTING COMPOUND THEREIN, AND LEAD WIRES FROM SAID COILEXTENDING THROUGH THE POTTING COMPOUND IN SAID SECOND HOUSING EXTERNALLYOF SAID SECOND HOUSING.